Embodiments of the invention relate generally to electric drive systems including hybrid and electric vehicles and to stationary drives that are subject to transient or pulsed loads and, more particularly, to transferring energy between an electrical storage device of the vehicle or drive and a power source external to the vehicle or drive.
Hybrid electric vehicles may combine an internal combustion engine and an electric motor powered by an energy storage device, such as a traction battery, to propel the vehicle. Typically, the electric motor is coupled between the internal combustion engine and the transmission to take advantage of the torque increase through the transmission. Such a combination may increase overall fuel efficiency by enabling the combustion engine and the electric motor to each operate in respective ranges of increased efficiency. Electric motors, for example, may be efficient at accelerating from a standing start, while combustion engines may be efficient during sustained periods of constant engine operation, such as in highway driving. Having an electric motor to boost initial acceleration allows combustion engines in hybrid vehicles to be smaller and more fuel efficient.
Plug-in hybrid vehicles are configured to use electrical energy from an external source to re-charge the traction battery. Such vehicles may include on-road and off-road vehicles, golf cars, neighborhood electric vehicles, forklifts, and utility trucks as examples. These vehicles may use either off-board stationary battery chargers or on-board battery chargers to transfer electrical energy from a utility grid or renewable energy source to the vehicle's on-board traction battery.
While hybrid vehicles offer many advantages, hybrid vehicles also include additional components not found in a conventional internal combustion vehicle. To convert a conventional vehicle to a hybrid vehicle, significant changes must be made to the vehicle chassis and the vehicle control system. For example, a hybrid vehicle includes a motor capable of driving the wheels and also operating as a generator when driven by the wheels. A hybrid vehicle also includes a controller to control power flow between the motor and an energy storage device. The hybrid vehicle controller may also receive driver commands that are used for control of conventional internal combustion engine vehicles and/or control of additional inputs related to hybrid mode of operation.
One method of converting a conventional vehicle to a hybrid vehicle includes integrating the controller utilized to control the hybrid components into the engine controller. While this method allows the modified engine controller to control both the engine components and the motor components, modifying the engine or engine controller is difficult and costly as engine controllers typically include a microprocessor to control the engine and vehicle functions. In order to modify the microprocessor, specialized tools and knowledge generally proprietary to the vehicle manufacturer is needed. Further, space constraints may limit the ability to couple an electric drive system between the engine and the transmission. As a result, modifying a conventional vehicle to a hybrid vehicle to take full advantage of the increased fuel efficiency of the hybrid vehicle system may be difficult and cost prohibitive.
It would therefore be desirable to provide an apparatus and method to convert a conventional vehicle to a hybrid vehicle that overcomes the aforementioned drawbacks.